1. Field of the Invention
The present invention relates to a wafer separating method for separating a wafer along a plurality of streets to obtain a plurality of individual devices, wherein the wafer is composed of a substrate and a laminated member formed on the substrate, and the laminated member is composed of an insulating film and a functional film laminated on the insulating film.
2. Description of the Related Art
As well known in the art, a semiconductor wafer having a plurality of devices such as ICs and LSIs arranged like a matrix on the upper surface of a substrate such as a silicon substrate is fabricated in a semiconductor device fabrication process, wherein each device is formed by a laminated member composed of an insulating film and a functional film laminated on the insulating film. In such a semiconductor wafer, the plural devices are partitioned from each other by a plurality of separation lines called streets preliminarily formed on the upper surface of the semiconductor wafer, and the semiconductor wafer is separated along these streets to obtain the individual devices.
The separation of the semiconductor wafer along the streets is usually performed by using a cutting unit called a dicer. The cutting unit includes a chuck table for holding a semiconductor wafer as a workpiece, cutting means for cutting the semiconductor wafer held on the chuck table, and moving means for relatively moving the chuck table and the cutting means. The cutting means includes a rotating spindle adapted to be rotated at a high speed and a cutting blade mounted on the spindle. The cutting blade is composed of a disk-shaped base and an annular cutting member mounted on the outer circumferential portion of a side surface of the base. The cutting member is formed by fixing diamond abrasive grains having a grain size of about 3 μm by electroforming, for example.
In recent years, a semiconductor wafer including a substrate such as a silicon substrate and a laminated member formed on the substrate for forming a plurality of devices such as ICs and LSIs has been put into practical use, wherein the laminated member is composed of a low-permittivity insulating film (Low-k film) formed of a vitreous material such as SiO2, SiO, and SiN and a functional film for forming circuitry, thereby improving the performance of each device.
The material of the Low-k film is different from the material of the substrate, so that it is difficult to simultaneously cut the Low-k film and the substrate by using the cutting blade. More specifically, the Low-k film is very brittle like mica, so that if the wafer is cut along each street by the cutting blade, there arises a problem such that the Low-k film may be peeled and such peeling may reach the circuitry in the functional film to cause a fatal damage to each device.
A wafer separating method intended to solve this problem is disclosed in Japanese Patent Laid-Open No. 2005-142389. This wafer separating method includes the steps of forming two laser cut grooves along each street formed on a semiconductor wafer to split a laminated member composed of an insulating film and a functional film and next positioning a cutting blade between the two laser cut grooves to relatively move the cutting blade and the semiconductor wafer, thereby cutting the semiconductor wafer along each street.
In this wafer separating method, a pulsed laser beam is applied along each street on the semiconductor wafer to melt and vaporize the laminated member along each street, thereby forming each laser cut groove. However, strain due to the laser processing remains on both sides of each laser cut groove, causing a reduction in die strength of each device separated from the semiconductor wafer.